Adhesive composition for bonding rubber to metal



No Drawing.

United States Patent 3,258,388 ADHESIVE COMPOSITION FOR BONDING RUBBERT0 METAL Elmer W. Coleman, Jr., Wilmington, Del., and Donald M. Alstadt,Erie, Pa., assignors to Lord Corporation,

a corporation of Pennsylvania Application Nov. 20, 1959, Ser. No.

854,231, which is a continuation of application Ser. No.

504,714, Apr. 29, 1955. Divided and this application Aug. 31, 1962, Ser.No. 220,889

Claims. (Cl. 161-418) The present invention relates to a novel adhesivecomposition especially suitable for bonding rubber to metal. Thisapplication is a division of application Serial No. 854,231 filedNovember 20, 1959, now abandoned, which application is a continuation ofapplication Serial No. 504,714 filed April 29, 1955, now abandoned.

There has been a Wide variety of materials suggested for use in bondingrubber to metal. Adhesives for this purpose have generally comprised acombination of a material which bonds readily to rubber with a materialwhich bonds to metal upon heating of the assembly under pressure. Singlematerials which bond to rubber well as to metal have also beendisclosed.

While in some of the prior art instances the adhesion provided betweenthe rubber and the metal is high, the general order of adhesion providedis moderate to poor. Moreover, the resistance to heat, solvents andmoisture of the bonds provided by the prior adhesives is not as great asis normally desired in commercial applications. Another limitation withthe use of these adhesive compositions is that the vulcanizingconditions under which bonding is effected must be very carefullycontrolled.

It is the principal object of the present invention to provide a noveladhesive composition for bonding rubber to metal.

Another object is to provide an adhesive for bonding rubber to metal bywhich the bond produced between the rubber and metal possesses improvedresistance to heat, solvents and moisture.

A further object of the invention is to provide an adhesive for bondingrubber to metal which bonding may be etfected under a wide variety ofvulc-anizing conditions.

Other objects will become apparent from a consideration of the followingspecifications and claims.

The method of the present invention comprises, in the bonding of rubberto metal involving interposing between the rubber body and metal body anintermediate phase adherable to metal and rubber and heating thecomposite structure under pressure, the. improvement which comprisesinterposing between said metal body and said rubber body an intermediatephase comprising a material adherable to metal and a poly-C-nitrosoaromatic compound.

It has been found that the useof a poly-C-nitroso compound, such as adi-C-nitroso, aromatic compound in conjunction with a rubber-to-metaladhesive results in an improved bond over What is obtained when thepoly-C-nitroso aromatic compound is not included. This is true generallyof any known type of rubber-to-metal adhesive. The improvement is somarked, in fact, that the adhesive material with which thepoly-C-nitroso aromatic compound is employed need not possess any normalbonding afiinity for rubber. In this case, the poly- C-nitroso aromaticcompound provides the bonding between the rubber body and theintermediate bonding phase. The reason why the poly-C-nitroso aromaticcompound results in such improved bonding between the rubber body andthe intermediate adhesive layer is not fully understood. It is believed,however, that, during curing of the assembly under heat and pressure,

3,258,388 Patented June 28, 1966 'ice the poly-C-nitroso aromaticcompound reacts with olefin chain structure with which it comes incontact, that is, the rubber body itself or a tie coat of olefinicmaterial on and merged with the rubber body. Since the remainder of thepoly-C-nitroso aromatic molecule is bound in the intermediate bondingphase, a chemical linkage between this phase and the rubber body isobtained. This theory is strengthened by the fact that if only a metaladherent which possesses no significant rubber adhesion properties isemployed in conjunction with the poly-C-nitroso compound, the rubberbody can nevertheless be bonded securely to the metal body.

All that is necessary, therefore, in accordance with the broader aspectsof the invention is that, in addition to the poly-C-nitroso compound, amaterial possessing metal adherent properties be present. In such a casethe intermediate bonding phase will comprise the metal adherent and thepoly-C-nitroso compound, the metal adherent being at least in contactwith the surf-ace of the metal body and the poly-C-nitroso compoundbeing at least in contact with the rubber body. According to thepractice of the invention disclosed and claimed in our copendingapplication Serial No. 220,890, filed August 31, 1962, a vulcanizableolefin discussed more in detail hereinaf-ter will also be employed,since the inclusion of the poly-C-nitroso aromatic compound in suchsystem provides or imparts thereto particularly marked adhesion betweenthe rubber and the metal.

Referring specifically to the poly-C-nitroso aromatic compound, it maybe any aromatic hydrocarbon, such as the benzenes, naphthalenes,anthracenes, biphenyls and the like, containing at least two nitrosogroups (NO) attached directly to non-adjacent ring carbon atoms. Thepresently preferred poly-C-nitroso are the di-C-nitroso compounds,especially the dinitroso benzenes and naphthalenes, such as the meta orparadinitr-osobenzenes and the metaor paradinitrosonaphthalenes and theinvention will be described more in detail hereinafter in terms of thedi-C-nitroso compounds although it will be understood that correspondingaromatic compounds containing three or more nitroso groups may beemployed. The nuclear hydrogens of the aromatic nucleus may be replacedby alkyl, alkoxyl, cycloalkyl, aryl, arylalkyl, arylamine, aryl nitrosoamine, halogen, and the like, groups. The presence of such substituentson the aromatic nucleus has little effect on the utility of thedi-C-nitroso compounds in the present invention and, as far as ispresently known, there is no limitation as to the character of thesubstituents, and they may be organic or inorganic in nature.- Hence,where reference is made herein to poly-C-nitroso or di-C-nitrosoaromatic compound, benzenes, or naphthalenes it will be understood toinclude such substituted derivatives as well as the unsubstituteddinitroso compounds, unless otherwise specified. Hydroxy substitutedd-i-C-nitroso aromatic compounds are stated in the literature torearrange with the nitroso group to form the oxime, and, hence, are notconsidered dinitroso aromatic compounds as herein defined. Orthodi-C-nitroso compounds also do not exist as such and, hence, are notincluded herein.

The preferred poly-C-nitroso aromatic compounds, as stated, are themetaor paradinitrosobenzenes and naphthalenes. In this connection, thecompounds falling within the following generic formula have been foundto be particularly advantageous:

where A is phenyl or naphthyl, where R is an alkyl, cycloalkyl, aralkyl,aryl, aryl amine or alkoxy group containing from 1 to 20 carbon atoms orhalogen and where n is O to 3. Of the substituted derivatives the alkylsubstituted derivatives are preferred. Examples of such substitutedaromatic di-C-nitroso compounds are:

p-Nitrosobenzene m-Dinitrosobenzene 2,5-dinitr0soparacymeneZ-methyl-1,4-dinitrosobenzene Z-methyl-S-chloro-1,4-dinitrosobenzene1,4-dinitrosonaphthalene 2-fiuoro-1,4-dinitrosobenzeneZ-methoxy-1,3-dinitrosobenzene S-chloro-1,3-dinitrosobenzene 2-benzyl- 1,4-dinitrosobenzene 2-cyclohexyl-1,4-dinitrosobenzene Referringspecifically to the metal adherent, it may be selected from a widevariety of organic materials, that is compounds and polymers, andmixtures thereof which possess adhesive properties toward metalcharacteristic of adhesives commonly employed in adhesive-bonded,structural, load-carrying fabrications of metal members with themselvesand other structural elements. Such materials possess, in the bondedassembly, a high order of bond strength, usually at least about 20pounds per lineal inch under stripping test, and a high order ofcohesiveness. The cohesive and adhesive properties of such materials inthe bonded assembly must be at least substan= tially equal to thecohesive strength of the rubber which is bonded to the metal, and suchcohesive and adhesive properties are developed under conditions commonlyemployed to vulcanize the rubber body stock. Organic compounds andpolymeric materials that adhere to metal surfaces in the above-discussedmanner are well known and include: (a) thermosetting condensationpolymers, such as thermosetting phenol-aldehyde resins, thermosettingepoxy resins, thermosetting polyester resins, thermosetting triazineresins, and the like; (b) polymers and coplymers of polar ethylenicallyunsaturated materials, such as polyvinyl butyral; polyvinyl formal;polyvinyl acetate; chlorinated polyvinylchloride; copolymers of vinylacetate and vinyl chloride; chlorinated copolymers of vinyl acetate andvinyl chloride, polymers of acrylic acid; copolymers of acrylic acid andconjugated dienes, such as butadiene-1,3,2-chlorobutadiene-1,2,2,3-dichlorobutadiene 1,3, and afterhalogenated products thereof; polymers of methacrylic acid; copolymersof methacrylic acid and con jugated dienes; copolymers of vinyl pyridineand conjugated dienes, and polyvalent acid reaction products thereof,and the like; (c) halogenated rubber, such as chlorinated natural rubberand chlorinated synthetic rubber; for example, chlorinatedpolychloroprene, chlorinated polybutadiene; chlorinated copolymers ofbutadiene and styrene; mixtures of chlorinated rubber withhydrohalogenated rubber or hypohalogenated rubber, and the like; (d)polyisocyanates, such as P,P' diisocyanato diphenyl methane,hexamethylene diisocyanate, P,P,P" triisocyanato triphenyl methane,3,3-dimethyl-4,4-biphenylene dissocyanate, 3,3'-dimethoXy-4,4'biphenylene diisocyanate, phosgenated aniline-aldehyde resins, such asthose disclosed in patent 2,683,730, and the like.

The rubber which may be bonded to metal in accordance with the presentinvention may be selected from any of the natural rubbers and olefinicsynthetic rubbers including polychloroprene, polybutadiene, neoprene,Buna- S, Buna-N, butyl rubber, grominated butyl rubber, and the like.The metals to which the rubber may be bonded may also be selected fromany of the common structural metals such as iron, steel (includingstainless steel), lead, aluminum, copper, brass, bronze, Monel metal,nickel, zinc, and the like.

In carrying out the method of the present invention, an intermediatephase comprising the di-C-nitroso compound and the metal adherent isinterposed between the surface of the rubber body and the surface of themetal body which it is desired to bond together. In the intermediatephase the di-C-nitroso aromatic compound will at least be available atthe interface between the rubber body and the intermediate phase, andthe metal adherent will at least be available at the interface betweenthe metal body and the intermediate phase. Such an intermediate phase isordinarily provided by the application of a mixture comprising thedi-C-nitroso aromatic compound and the metal adherent. The intermediatephase may also be provided, however, by applying the componentsseparately. In connection with this latter embodiment, any one ofseveral procedures may be followed, including applying the di-C-nitrosoaromatic compound to the rubber surface and the metal adherent to themetal surface; applying the metal adherent to the metal surface afterwhich the di-C-nitroso aromatic compound is applied thereover, or thedi-C-nitroso aromatic compound may be applied to the rubber surfacefollowing which the metal adherent may be applied thereover. Variouscombinations of these means may be employed, such as the application ofa mixture high in di-C-nitroso aromatic compound and low in metaladherent, to the rubber body and the application of a mixture ofdi-C-nitroso compound and metal adherent high in metal adherentthereover or to the metal body. The exact procedure followed is notcritical, the important factor being the interposition between therubber and the metal to be bonded of an intermediate phase comprisingthe di-C-nitroso aromatic compound and a metal adherent, thedi-C-nitroso aromatic compound being at least available to the rubberfor adhesion to the rubber and the metal adherent being at leastavailable to the metal for adhesion to the metal.

As stated in accordance with the invention disclosed and claimed in ourcopending application, Serial No. 220,890, filed August 31, 1962, thereis also employed a readily vulcanizable olefin such as thepolybromobutadienes, the polychlorobutadienes, and partiallyafterhalogenated products thereof, partially afterhalogenated copolymersof isobutylene and butadiene, particularly those partiallyafterbrominated copolymers disclosed in US. Patent 2,631,984, thepolycyanobutadienes, the polynitrobutadienes, polycyclopentadiene,tetrachlorocyclopentadiene, partially hydrohalogenated rubbers,partially hypohalogenated rubbers, and the like. Such olefins arereadily vulcanizable, that is to say, they are more vulcanizable thanpolybutadiene. Preferably, the olefin employed is at least asvulcanizable as poly 2-chlorobutadiene-1,3. Particularly advantageousolefins in this regard are polychloroprene (poly-2-ch1orobutadiene-1,3),poly 2,3-dichlorobutadienel,3 and after-brominated poly2,3-dichlorobutadiene-1,3, such as those containing a bromine content ofbetween about 7.5 and about 42 mol percent, preferably between about 15and about 36 mol percent.

When a vulcanizable olefin is employed as part of the intermediatebonding phase it may be applied in admixture with the di-C-nitrosoaromatic compound, only, or in admixture with the di-C-nitroso aromaticcompound and metal adherent. Since the vulcanizable olefin, when used inthe intermediate bonding phase, is primarily for the purpose offostering adhesion with the rubber it will at least be available at theinterface between the rubber body and the intermediate bonding phase.When the three main components are applied in admixture to the rubber ormetal surface, the olefin and, of course, the di-C-nitroso aromaticcompound, will be available to the rubber surface, and the rubberadherent will be available to the metal. A mixture of only the olefinand di-C-nit-roso aromatic compound may also be applied to the rubbersurface or to a previously applied film containing the metal adherent onthe metal surface;

As is well known in the art, it is often desirable to provide a tie coator layer between the adhesive bonding phase and the actual rubber body.Such a tie coat may be employed in accordance with the presentinvention. The tie coat normally comprises a rubber, either a natural orsynthetic rubber or rubber-like material, or a vulcanizable olefin ofthe type discussed above, and may be applied either to the rubbersurface or over the adhesive layer, such as in the form of a solution oras a preformed sheet. Such-tie coats are selected on the basis of therubber body and adhere well thereto. The enhanced adhesion to the rubberbody afforded through the use of the di-C-nitroso aromatic compound inaccordance with the present invention is applicable here in fosteringadhesion between the bonding phase and the tie coat. In view of this andsince the tie coat is merged with the rubber body it is consideredherein as part of the rubber body. Thus, where reference is made torubber body or surface of the rubber body, it will be understood torefer equally to the rubber body proper when no tie coat is employed andto the merged rubbed body tie coat when a tie coat is employed.

Reference has been made hereinabove to the application of the variouscomponents of the adhesive bonding phase to one or the other or both ofthe surfaces to be joined. The particular mode of application is notcritical insofar as the broader aspects of the invention are concerned,and one or more of the components may be applied in solid, finelydivided form, or in liquid form, most-advantageously the latter. Whenapplied in liquid form, one or more of the components, which is aliquid, may serve as the vehicle, or a solvent for one or more of thecomponents may be employed. The application of the various components inthe form of a solution of at least one of them is preferred. In thisconnection it is generally preferred that the metal adherent, andvulcanizable olefin when employed, be in solution whereas thedi-C-nitroso aromatic compound may merely be suspended in such solution.Such solution is included herein and in the claims where reference ismade re the application of the composition in the form of a solution.-As solvent there may be employed any organic liquid or mixtures thereofin which one or more of the ingredients to be applied is soluble to theextent dictated by the viscosity of the solution and the exact means ofapplication to be employed. Generally, the solids content of such asolution may range from as low as about 5% to as high as about 30%,although in most cases, where the composition will be applied inbrushing, the solids content will range between about and about 25%. Anysolvent employed should also be readily volatile so that lengthy dryingperiods are not encountered. The preferred solvents, especially for thepreferred compositions discussed hereinafter, are aromatic hydrocarbons,such as benzene, toluene, xylene, and the like, and the chlorinatedaromatic hydrocarbons such as monochlorobenzene, dichlorobenzene, andthe like. Small amounts of aliphatic hydrocarbons, chloroaliphatichydrocarbons, ketones, ethers and/or alcohols may be included ifdesired.

After the adhesive component or components have been applied asdescribed above and any solvent evaporated, the rubber surface and themetal surface which are to be bonded are brought together and theassembly heated under pressure to cause vulcanization of the rubberstock and bonding. As is well known in the art, the exact time andtemperature of curing will vary depending upon the nature of the bodyemployed as Well as on the nature of the ingredients in the adhesivephase. In general, however, the temperature during curing will bebetween about 270 F. and about 350 F. and the curing time will rangefrom about 20 to about 60 minutes.

As a general purpose adhesive requiring but a single application ofmaterials, it is generally preferred to employ a mixture of all thematerials to be present in the intermediate bonding phase, namely, amixture of the di-C-nitroso aromatic compound and the metal adherent,

and also the vulcanizable olefin, when employed. In any mixture of thedi-C-nitroso aromatic compound will be effective in amounts as low asabout 1%, by weight, based on the weight of the solids. Amounts of di-C-nitroso aromatic compound greatly in excess of that amount-even as highas -95% may be employed. The metal adherent is also effective inrelatively low levels such as about 5% and it may be present in amountsas high as about 94%, by weight, based on the weight of the solids inthe mixture. When the olefin is employed, the amount thereof may varywidely from as low as about 5% to as high as about 94%, on the samebasis.

Referring specifically to the di-C-nitroso aromatic com pound, thefunctional portion of this material is the nit-roso groups themselves.Hence, in any inter-mediate bonding phase of the present invention theamount of nitroso groups at least available to the rubber surface isimportant. In general, sufiicient of the di-C-nitroso compound will beemployed so that nitroso groups make up at least about .4% of the solidsin the intermediate bonding phase at least adjacent the rubber surface.The amount of di-C-nitroso aromatic compound employed may be well abovethis figure, and may go as high as that providing about 42%, by Weight,of nitroso groups in the solids of the intermediate bonding phase atleast adjacent the rubber surface.

Particularly advantageous metal adherents for use in admixture with thedi-C-nitroso aromatic compound (and also with an olefin if employed) arethe chlorinated rubber-s. Especially advantageous olefins for use insuch a mixture are polymers of chlorine-substituted butadiene such aspolychloroprene, 2,3-dichlorobutadiene-l,3 and the after-brominatedpolymers of 2,3-dichlorobutadiene 1,3 of the type mentioned above.

The following examples are given to illustrate the invention and are notintended to limit the scope of the invention in any way inasmuch as therelative proportions may vary and the ingredients may be substituted byothers which perform the equivalent function to those given.

Example I An adhesive consisting of 50 parts 2,3-dinitrosoparacymene, 50parts soluble, fusible, acid-catalyzed phenolformaldehyde resin, 4 partshexamethylenetetramine, and 125 parts of a mixture of equal partsmethanol and methyl ethyl ketone is brushed on a strip of degreased,gritblasted, cold-rolled steel, 2% x l, and allowed to dry for about 30minutes. A A" slab of unvulcanized natural rubber compound consisting ofparts smoked sheet, 40 parts channel black, 10 parts zinc oxide, 2.5parts sulfur, 0.5 part 2-mercaptobenz-othiazole, 0.5 part benzothiazyldisulfide, 0.2 part zinc diethyl dithiocarbamate', 2 parts pine tar and1.5 parts phenyl-beta-naphthylamine, is applied to the adhesive-coatedsurface. The rubbera dhesive coated metal assembly is vulcanized 30minutes at 312 F. The bond which results is such that the rubber cannotbe stripped from the metal without tearing into the body of elast-omer.

Example II An adhesive consisting of 50 parts paradinitrosobenzene, 50parts polyvinyl butyral (XYHL grade) and 333 parts methanol is employedin the manner described in the foregoing example. The natural rubbercompound used in Example I is employed and the assembly is vulcanizedunder pressure for 20 minutes at 320 F. The bond which results in suchthat the rubber cannot be stripped from the metal without tearing intothe body of elastomer.

Example 111 An adhesive consisting of 10 parts 2,5-paradinitrosocymene,30 parts poly 2,3-dichlorobutadiene-1,3 (40 C. emulsion polymer,conversion approximately 90%), 70

essed in the manner of the foregoing examples.

7 parts chlorinated natural rubber (125 CPS grade) and 300 parts tolueneis applied to the steel surface and proc- The natural rubber compoundused in Example I is employed and the assembly is vulcanized underpressure for 30 minutes at 312 F.

An adhesive similar to the above except that it contains no nitrosocompound is processed along with the nitroso-containing cement.

Adhesion is measured in both cases by a method similar to that describedin ASTM testing specification D429-47T, Method B. In this test, therubber is peeled or stripped from the metal at an angle of 90 and theadhesion recorded in pounds per inch. The assembly produced with themixture of chlorinated rubber and poly chlorobutadiene pulls 22 poundsper inch. The nitrosocontaining adhesive assembly pulls 52 pounds perinch and tears substantially into the body of the elastomer indicating abond strength of more than twice that of the control adhesive.

Example IV An adhesive consisting of 15 parts paradinitrosobenzene, 30parts after-brominated poly 2,3-dichlorobutadiene-1,3 (approximately 27mol percent Br), 70 parts chlorinated natural rubber (125 CPS grade) and300 parts toluene is applied to the steel surface and processed in theabove-described manner. The elastomer employed is a butyl rubber (GR-I)compound consisting of 100 parts base polymer, 54 parts SRF black, partszinc oxide, 2 parts sulfur, 1 part tetraethylthiuramidisulfide and 0.5part 2-mercaptobenzothiazole. The elastomer-adhesive coated metalassembly is vulcanized under pressure for 25 minutes at 307 F.

A binary mixture of the chlorinated rubber and brominatedpolychlorobutadiene is processed along with the nitroso-containingadhesive.

Adhesion is measured as in Example III. The binary mixture ofchlorinated rubber and brominated polychlorobutadiene pulls 12 poundsper inch. The nitroso-containing adhesive pulls 95 pounds per inch,almost an eight-fold improvement over the control adhesive.

Example V An adhesive consisting of parts paradinitrosobenzene, 30 partsafter-brominated poly 2,3-dichlorobutadiene-1,3 (approx. 27 mol percentBr), 70 parts chlorinated natural rubber (125 CPS grade), and 300 partstoluene is applied to the steel surface and processed in theabovedescribed manner. The elastomer employed is a standard GR-Scompound consisting of 100 parts base polymer, 50 parts HAF black, 3parts zinc oxide, 2 parts stearic acid, 1.8 parts sulfur, 1 partN-cyclohexyl-Z-benzothiazole sulfenamide, 1.25 partsphenyl-beta-naphthylamine and 10 parts rosin. The elastomer-adhesivecoated metal assembly is vulcanized under pressure for 30 minutes at 288F.

A binary mixture of the chlorinated rubber and brominatedpolychlorobutadiene is processed along with the nitroso-containingadhesive.

Adhesion is measured as in Example III. The binary mixture ofchlorinated rubber and brominated polychlorobutadiene produces adhesionof 38 pounds per inch, separating between the adhesive and theelastomer. The nitroso-containing adhesive assembly pulls 73.5 poundsper inch, tearing into the body of elastomer.

Example VI An adhesive consisting of 20 parts 2,5-dinitrosoparacymene,30 parts after-brominated poly 2,3-dichlorobutadiene-1,3 (approx. 27 molpercent Br), 70 parts chlorinated natural rubber 125 CPS grade) and 300parts toluene is applied to the steel surface and processed in theabove-described manner. A binary mixture of the chlorinated rubber andchlorobutadiene is processed along with the nitroso-containing adhesive.The elastomer employed is a natural rubber compound consisting of partssmoked sheet, 5 parts channel black, 15 parts lead oxide, 10 parts zincoxide, 2.5 parts 2-mercaptobenzothiazole, 1.5 parts sulfur, 2 partsphenyl-beta-naphthylamine, 2 parts pine tar and 2 parts wax. Theelastomeradhesive coated assembly is vulcanized under pressure for 30minutes at 288 F. The laminate produced with the binary mixture can beseparated, the failure occurring between the cement and the rubber. Theadhesion produced with the nitroso-containing adhesive is such that therubber cannot be stripped from the metal without tearing into the bodyof the elastomer.

Examples VIII through XI illustrate the use of two-coat adhesivesystems.

Examples VII through XL-Elastomer compounds Natural rubber: Parts Smokedsheet 100 High abrasion furnace black 50 Zinc oxide 15 Stearic acid 1Sulfur 2 Benzothiazyl disulfide 1.5 Zinc dimethyl dithiocarbamate 0.2

Neoprene:

Neoprene type WRT 100 Fine furnace black 50 Zinc oxide 5 Magnesium oxide4 Stearic acid 0.5 2-mercaptoimidazoline 0.5

GR-S:

GR-S (standard) 100 Channel black 60 Zinc oxide 5 Sulfur .35Tetraethylthiuramidisulfide 3.5

In each case the secondary cement consists of 100 parts after-brominatedpoly 2,3-dichlorobutadiene-l,'3 (approximately 27 mol percent Br), 20parts 2,5-dinitrosoparacymene and 300 parts toluene. The primer coatsare applied to degreased, grit-blasted steel and allowed to dry forapproximately 30 minutes. The secondary cements are then applied overthe primer coat and allowed to dry. The indicated elastomer compound isthen applied to the adhesive coated metal and the assembly vulcanizedunder pressure for 30 minutes at 307 F. The bonds thus formed are ofsuch strength that in all cases attempts to strip the rubber from themetal result in failure of the body elastomer.

Composition of Metal Priming Coat %lastomer mployed Example VII:

100 parts ketone soluble, base catalyzed, solid, thermosetting resinousphenol-aldehyde condensate. 200 Neoprene. parts methyl ethyl ketone.Example VIII:

100 parts polyvinyl butyral, XYHL grade Natural 666 parts methanolrubber. Example IX:

100 parts chlorinated neoprene (chlorine 67%, viscosity 20% solution intoluene, CPS at 25 0.). D0. 300 parts toluene Example X:

100 parts P,P',P-triisocyanate triphenyl methane GR 8 300 partsmethylene chloride i oo t hl t d l l hl d (V par s c orma e po yviny cori e inyon N) 400 parts monochlorobenzene lNeoprene' Example XII Anadhesive consisting of 75 parts chlorinated rubber (125 CPS grade), 25parts paradinitrosobenzene and 300 parts toluene is used to bond steeland freshly sheeted unvulcanized natural rubber compound consisting of100 parts smoked sheet, 30 parts channel black, 15 parts zinc oxide,2.75 parts stearic acid, 3 parts sulfur, 0.6 part tetramethyl thiurammonosulfide, 2 parts pine tar and 0.75 part phenyl-beta-naphthylamineunder the conditions set forth in Example I. The same is done for anadhesive consisting of 75 parts chlorinated rubber (125 CPS grade), 25parts sulfur and '300 parts toluene. Adhesion is measured in pounds perinch. The sulfur-containing mix produces a bond pulling at 17 pounds perinch. The nitrosobenzene-containing mix produces a bond pulling at 86pounds per inch.

Example XIII An adhesive consisting of 50 parts p-dinitrosobenzene, 50parts alkylene oxide-bisphenol. A derivative esterified with fumaricacid, 1.5 parts benzoyl peroxide, 0.5 part cobalt naphthenate, 140 partstoluene and parts methyl ethyl ketone is applied to a degreased,grit-blasted steel surface and allowed to d-ry for approximately onehour. A slab of freshly sheeted unvulcanized natural rubber compoundconsisting of 100 parts smoked sheets, 30 parts channel black, partszinc oxide, 2.75 parts stearic acid, 3 parts sulfur, 0.6 parttetramethyl thiuram monosulfide, 2 parts pine tar, and 0.75 partphenyl-beta-naphthylamine is applied to the adhesive-coated surface andthe assembly vulcanized under pressure for 30 minutes at 312 F. The bondwhich results is such that the elastomer cannot be stripped from themetal without tearing into the body of the elastomer.

Example XIV An adhesive consisting of 50 parts p-dinitrosobenzene, 35parts epichlorohydrin-bisphenol A condensate (epoxide equavalent ofapproximately 900-1000), 15 parts phthalic anhydride and 150 partsmethyl ethyl ketone is applied to a degreased anodized duraluminumsurface and allowed to dry for approximately one hour. A slab of freshlysheeted unvulcanized natural rubber compound of the type employed inExample XIII is applied to the adhesive coated surface and the assemblyvulcanized under pressure for 30 minutes at 312 F. The bond whichresults is such that the elastomer cannot be stripped from the metalwithout tearing into the body of the elastomer.

While the compositions disclosed and claimed herein are especiallyuseful in the bonding of rubber to metal, individual species thereofhave other uses due to their film-forming and adhesive properties.

Considerable modification is possible in selecting the di-C-nitrosoaromatic compound and metal adherent, and reactive olefin, and amountsthereof without departing from the scope of the present invention.

What is claimed is:

1. An adhesive composition for bonding rubber to metal comprisingchlorinated rubber and at least 1%, by weight, of a poly-C-nit-rosoaromatic compound.

2. An adhesive composition for bonding rubber to metal comprisingchlorinated rubber and at least 1%, by weight of a di-C-nitroso aromaticcompound.

3. An adhesive composition for bonding rubber to metal comprisingchlorinated rubber and at least 1%, by weight, of a di-C-nitrosoaromatic compound selected from the group consisting ofdinitrosobenzenes and dinitrosonaphthalenes.

4. An adhesive composition for bonding rubber to metal comprisingchlorinated rubber and at least 1%, by weight, of p-dinitrosobenzene.

5. An adhesive composition for bonding rubber to metal comprising asolution of chlorinated rubber and at least 1%, by weight, of adi-C-nitroso aromatic compound based on the weight of the solids.

6. An adhesive composition for bonding rubber to metal comprising asolution of chlorinated rubber and at least 1%, by weight, of adi-C-nitroso aromatic compound based on the weight of the solids, saidsolution having a solids content of from about 5 to about 30 percent, byweight.

7. An adhesive composition for bonding rubber to metal comprising asolution of chlorinated rubber and at least 1%, by weight, of adi-C-nitroso aromatic compound based on the weight of the solids, saidsolution having a solids content of from about 10 to about 25 percent,by weight.

8. An adhesive composition for bonding rubber to metal, comprising asolution in an aromatic solvent, of chlorinated rubber and at least 1%,by weight, of a di-C- nitroso aromatic compound based on the weight ofthe solids.

9. An adhesive composition according to claim 8 in which saiddi-C-nitroso aromatic compound is pdinitrosobenzene.

10. The method of bonding rubber to metal which comprises interposingbetween said rubber and metal an intermediate layer comprisingchlorinated rubber and at least 1%, by weight, of a poly-C-nitrosoaromatic compound, and heating the resulting composite structure underpressure to vulcanize said rubber and bond said rubber to the metal.

11. The method according to claim 10 in which said rubber comprisesunvulcanized natural rubber.

12. The method according to claim 10 in which said rubber comprisespolybutadiene.

13. The method of bonding rubber to metal which comprises interposingbetween said rubber and metal an intermediate layer comprisingchlorinated rubber and at least 1%, by weight, of a di-C-nitrosoaromatic compound, and heating the resulting composite structure underpressure to vulcanize said rubber and bond said rubber to the metal.

14. The method according to claim 13 in which said rubber comprisesunvulcanized natural rubber.

15. The method according to claim ,13 in which said rubber comprisespolybutadiene.

References Cited by the Examiner UNITED STATES PATENTS 2,183,342 12/1939Williams 260-760 2,548,505 4/1951 Turner 26085.1 X 2,581,920 1/1952 Kuhn156-333 X 2,631,953 3/1953 Hubbard et al 161-221 2,690,780 10/ 1954Cousins.

2,900,292 8/1959 Coleman et al. 161-218 X 2,905,582 9/1959 Coleman etal. 156-331 X 3,053,712 9/1962 Grabowski 156-333 OTHER REFERENCESRehner, 1., Jr., and Flory, P. J., Vulcanization Reactions of ButylRubber, in Rubber Chemistry and Technology, vol. 19, October 1946, pages904-907.

EARL M. BERGERT, Primary Examiner.

CLIFTON B. COSBY, Examiner.

1. AN ADHESIVE COMPOSITION FOR BONDING RUBBER TO METAL COMPRISINGCHLORINATED RUBBER AND AT LEAST 1%, BY WEIGHT, OF A POLY-C-NITROSOAROMATIC COMPOUND.